Centrifugal pump



Fe. zo, 1940. J. MANN j 2,1%670` CENTRIFUGAL PUMP Fild July 9, 1957 gsheets-sheet 1 TTURIEY- Patented ret.2o,194o A 2,190,670

UNITED STATES PATENT ori-ICE CENTEIFUGAL PUNIP John Mann, seneea Falls,N. Y., assigner te Goulds Pumps, Inc., Seneca Falls, N. Y., acorporation of New York Appueatien July s, 1931, serial Ne. 152,801

2 claims. (ci. 10s-97) My invention relates to new and useful impump,within limits, may be readily varied While provements in centrifugalpumps. still mainttaining the pump at relatively high ef- Heretofore ithas been necessary for a manuciency, whereby without maintaining anabnorfacturer of pumping equipment, if he wished to mally large stock ofpumps,`a wide range of operl 5 compete with his competitors in thematter of ating conditions may be met.

quick deliveries upon orders received, to maintain Another object of myinvention is to provide a a large stock of -pumps on hand. Usually thecentrifugal pump Which'may be readily conmanufacturer keptin stock arange of sizes of verted into a pump having different operating pumpcasings and an innumerable number of characteristics. l pump impellers,each having different operatingl Another object of my invention is toprovide a 10 characteristics. Upon receipt of an order for a centrifugalpump so constructed and arranged pump, in accordance with certainspecifications, that the fluid capacity and pressure head, of themanufacturer selected the proper size of caswhich the pump is capable,may be varied over ing and mounted therein the impeller most nearratherwide limits. l ly adapted to obtain the characteristics, as to Anotherobject of my invention is to provide 15 fluid capacity and pressurehead, required. Not means whereby the volute of the casing, into onlydid this compel the manufacturer to mainwhich liquid is discharged bythe impeller vanes, tain a large inventory of pump casings and immay bevaried in volumetric'capacityand'in cross pellers, but also,particularly in the case of pumps sectional area, particularly at thethroat thereof,

for small capacities, the emciency of the average. to thereby vary theuid capacity and pressure 20v resulting pump was comparatively lowbecause a head of the pump. pump and its impeller for the best operatingchar- Another object of my invention is to provide a acteristics andelciency, must be designed for small capacity relatively high pressurecentrifueach other. The maintenance of a large stock of gal pump whichis eiicient in operation and which, 2d pump casings and impellers is adistinct hardmay be manufactured and sold at a reasonable 25 ship on themanufacturer and is particularly neccost. essary in pumps for smallcapacities because My invention further contemplates the provithecustomer, dueto the small size of the pump, sion of novel means forsealing the impeller drive expects shipment substantially upon receiptof shaft to protect the shaft from the-corrosive and t@ the order.abrasive action of the liquid being pumped.

In addition, centrifugal pumps, except centrif- My invention, inaddition, contemplates the ugal pumps of special design, in the pasthave provision of means for minimizing leakage from been primarily usedwhere a large volume of liqvthe high to the low pressure side of the'pump, uid was to be pumped at reasonably low pressures whereby toincrease the emciency thereof. or where a small volume of liquid was tobe Other objects and advantages of my invention 35 pumped at relativelylow pressures. Where v'will be more apparent from the following dehigherpressures were desired, particularly at scription when takeninconnection with the alcsmall capacities, other types of pumps havebeen companying drawings, in which:

used-usually a positive displacement pump. Figure 1 is a view showingthe pump and motor 40 Probably, the reason why centrifugal pumps haveassembly. 40 very rarely been used for small capacities, 100 Figure 2 isa sectional view showing thepump gallons per minute or less, atrelatively high prescasing, the impeller, the stuiiing box assemblysures, one hundred and fifty to two hundred and and other parts of mynovel pumping unit. op iifty feet totalhead, is because the leakage fac-Figure 3 is a view taken on the line 3-3 of tor, while relativelyunimportant in large capac- Figure 2.

45 ity pumps, is a significant factor in reducing the Figure 4 is apartial View, similar to that of efficiency of small capacity pumps. Toprovide an Figure 3, showing the cover plate of the pump eiiicient smallcapacity centrifugal pump capable casing rotated to decrease the crosssectional area of developing relatively high pressures required a of thecasing volute.

hand-tailored pump, the manufacturing expense Figure 5 is a developmentof the pump casing 50 of which did not admit of its being sold incomvolute. petition with other types of pumping equipment. Figure 6 is aview taken on the line 6-6 of An object of my invention is to provide acom- Figure 2 showing the manner in which the wearpact pumping unit soconstructed and arranged ing rings are locked in the casing. l that thefluid capacity and pressure head of the Figure 'I is a view taken on theline 1-1 of 55 rI'he features of my invention, while/they may,

for the most part, be embodied in any type of centrifugal pump, areparticularly adapted for incorporation in what is known in the art as aclose coupled pump. The primary differences between a close coupled pumpand other types of centrifugal pumps are that, in a close coupled pump,the motor and pump casings are, by what is known as an adapter, rigidlysecured closely together and the drive shaft is common to both the motorand the pump.

As shown in Figure 1, the assembly, in which the novel featuresof myinvention are incorporated, comprises a motor H having suitablepedestals l2 by which the unit may be supported on the oor or othersupport, an adapter I3 and a pump casing generally indicated by thenumeral v H3. The adapter is provided with hand holes to enable accessto the stuiiing box unit. The adapter, as shown in Figure 2, is rigidlybolted, as indicated at it, to the motor casing, and the pump casing isin turn rigidly bolted, as indicated at il, to the adapter. A thirdpedestal It is provided for supporting the unit on the oor or othersupport. Any suitable means may be provided for rigidly securing thepump and its motor to the floor, no special foundation being requiredwith this type of pump. If desired, the pump unit may be secured in avertical position as the unit is particularly adapted to operate in amrposition.

The pump casing comprises a casing proper i9 anda cover plate 2i whichmay be bolted thereto as indicated at 22. The shaft 23, which is commonto both the motor and pump, has a suitable bearing 2S at the pump end ofthe motor casing and another bearing (not shown) at the other end of themotor casing. That portion of the shaft 23 which extends beyond themotor casing H is overhung and extends through the adapter and into thepump casing i4. To the end of the shaft 23, by means of a key 2&1, issecured, against rotation with respect to the shaft, the hub 26 of arrimpeller 2l. The impeller is usually made of bronze and is held inposition on the shaft by means which will be later described.

The impeller comprises a web 2t, a plurality of vanes 29 cast integrallywith the web 2d and a shroud 3l which may be riveted or otherwisesecured to the varies, as indicated at 32. While I have shown anddescribed the impeller as being made in separate parts and then securedtogether, it will be appreciated that the web,vthe blades and the shroudmay be cast integrally. The main advantage of casting the web and theshroud separately is to enable the impeller to be more easily machinedor filed to provide smooth water passages. Ii the impeller is ratherwide, ci course, it may be more cheaply cast integral.

The shroud, as it approaches the impeller' anis, curves outward asindicated at Et to form a smooth entrance for fluid into the impeller,conimonly called the eye of the impeller. At its central portion, theshroud is anged outward, as

indicated at 3d, to provide a duid entrance or suction opening into theimpeller. The suction pipe 36 is threaded, as indicated at 3i, in anopening in the cover plate 2| and is in axial alignment with the ange 3dof the impeller so that fluid being drawn through the suctionvpipe, orowing thereto vby gravity, will smoothly enter the eye o f the pumpimpeller. ,If desired, instead of using threaded connections between thesuction pipe and the cover plate, flanged connections may be used.

The cover plate 2i has an inwardly directed flange 38 which ispreferably formed on the arc of a circle and which extends substantiallythree fourths of the distance around the cover plate, as shown in Figure3. This ange is of such width that, when the pump is assembled, its edgebutts against the wall 39 of the casing proper I9. The impeller 2l isconcentric with and somewhat smaller in diameter than the flange 38 toprovide clearance di around the impeller. The internal bore of thecasing proper i9 and the flange 38 are concentric except that the casingwall, beginning at the point t2, merges -into what is known in the artas a casing volute 60. The volute portion of the casing is in opencommunication with the impeller, extends from the point 42 and graduallyincreases invwidth and depth to the point t. The volute may be eitherrounded in cross section or substantially square as shown at d5 inFigure 2. The function of the casing volute is to convert the velocityhead of the liquid, imparted to it by the impeller, into pressure head.From the point i3 the volute merges smoothly into a discharge opening itformed in the casing proper i9. The point of merger of the volute withthe discharge outlet is known as the throat of the volute or the pointof cut water. The discharge opening el@ is substantially circular incross section, the cross sectional area gradually increasing toward theoutlet. In the discharge opening, in any suitable manner, is secured adischarge pipe d.

In my close coupled pump, the discharge pipe et may be located in anyone of four positions. Two of the positions are indicated in Figure 3,one in solid lines and the other in dotted lines.

This may be accomplished by shifting the entire u pump casing ifi withrespect to the adapter i3 and bolting the pump casing to the adapter inthe desired location by means of bolts one of which is indicated at ll.The fact that the entire pump casing may be shifted to dierent dischargepositions is of particular advantage in enabling the discharge pipe tobe secured to the discharge opening of the pump conveniently and with asfew bends in the discharge pipe as need be.

`The capacity of a pump and the pressure of liquid which it is capableof developing are known in the art as the characteristics of a pump.When the capacities and heads of which the pump is capable are plottedon graph paper, there is obtained what is known as a pump head-capacitycharacteristic curve. One of the features of my l invention is the meansby which the pump oi 3 my invention may be converted, withoutsubstituting any new parts or modifying any cf the parts of the pump,into a pump having diierent '57d operating characteristics or rather apump for' `as pump characteristic curves.

the cover plate to the casing proper in the desired location by means ofthe bolts, indicated at 22.

Shifting the cover plate in av clockwise direction, as viewed in Figure3, moves the flange 38 so as to decrease the area of the throat of thevolute or the maximum cross sectional area of the volute 48 an'd, ofcourse, its volumetric capacity. A position to which the flange 38 maybe shifted has been shown in Figure 4. From that figure, it will beapparent that the area at 48, the throat of the volute or the point ofcut-water, is less than the area at 43 of Figure 3, the point ofcut-water with the iiange in its normal position. It will further beapparent from Figures 3, 4 and 5, the latter of which is a developmentof the volute, that "the area at the throat of the volute, by properlypositioning the flange 38, may be made any desired amount. The dischargeof water from the pump may even be entirely cut oif by shifting theflange 38 in a clockwise direction so that the point 38 of the ange isshifted to or beyond the point 42 of Figure 3.

The practical effect of decreasing the throat area of the volute may bemade clear from Figure 10 whichy shows what have been described above yWe will assume that curve A is the head capacity curve of the pumpdescribed above and shown in the draw,- ings with the flange 38 in theposition shown in Figure 2; that is, with the throat area at itsmaximum. The pump casing and impeller are designed to obtain maximumpump efliciency with maximum volute throat area. Curve B, we willasvalve or, in other words, varying the pump discharge pipe opening andby proper measurements, well known in the art, determining variousheadcapacity points and brake horsepower points which areplotted ongraph` paper. After suiiicient points have been plotted, curve A,representing the head-capacity characteristic curve, and curve C,representing the brake horsepower, are drawn. From these two curves, theefficiency of the pump may be calculated for any condition by formulae,not necessary to be set forth herein.

Considering curve A, any condition along line A may be obtained byregulating or throttling the discharge valve, indicated at 49. Forexample, by properly regulating the discharge valve, the

' pump may be set to deliver forty-eight gallons per minute against atotal head (static head plus friction) of seventy feet. This conditionis shown at point D on curve A. Under/these conditions, the eiiiciencyof the pump and the brake horsepower required to drive the pump, foundon curves B and C directly below point D, will be respectivelyapproximately 52% and 1.6 horsepower. I

In the centrifugal pumps of the prior art, if conditions of head andcapacity were specied by the customer not found on curve A, another pumpwould have to be used-one having different operating characteristics,although there are several ways, not necessary to be described herein,of changing, within limits, the characteristics of a given pump.

My invention involves varying the characteristics of a pump by changingthe throat area of the volute. This is accomplished in the pump of myinvention, as stated above, by shifting the position of the point 38' ofthe ange 38. The effect of this may be made more clear from aconsideration of Figure 10. We will assume that E. IF and G are thehead-capacity, emciency and brake horsepower curves, respectively, ofthe pump described above with the fiange 38 in the position shown 1nFigure 4, in which position the volute throat area is considerably lessthan when the flange is in the position shown in Figure 2. By throttlingthe pump with the flange in the position shown in Figure 4, anycondition of head-capacity can be obtained along the curve E. Forexample, let us assume that, instead of the conditions 48 gallons perminute at 70 feet total head given above, a customer had desired a pumpcapable of delivering 16 gallons per minute at a total head of 'Z0 feet.This rcondition appears on the curveE at the point H. Reading below thepoint H on the curves F and G, it is found that the brake horsepowerrequired to drive the pump is approximately .9 horsepower and theefliciency of the pump is approximately 32%.

It will now be appreciated that, with the same casing and impeller, byshifting the flange 38 to the proper position, various characteristiccurves similar to curve E may be obtained. This eliminates the necessityof maintaining a large stock of pump casings and impellers on hand. Witha limited number of pumps in stock, a wide krange of operatingcharacteristics may be obtained. Moreover, it is possible by myinvention to make the volute throat exceedingly small in area, withoutthe necessity of attempting to cast volutes with small throat areaswhich is impractical. In practice, casingsl with small volute throatareas cannot be cast and must be machined.

One of the most important factors adversely aiecting the efliciency of acentrifugal pump is the leakage of liquid which occurs from the highpressure side of the impeller to the low pressure side thereof; that is,between the impeller flange 34 and the casing from the space 5Isurrounding the impeller to the suction inlet. The energy applied tothis leakage liquid is wasted.4 To minimize this leakage and to preventcasing wear, it is customary to employ what are known in the art ascasing wearing rings. These casing wearing rings are usually tted to andrigidly held in the casing and the impeller rotates with respect tothem.

In my pump construction, to limit the amount of leakage, I employ awearing ring 52 of novel design. Pump wearing rings are usually made ofbronze, although other materials can and have been employed. The wearingring 52 is generally L-shaped in cross section, as shown in Figure 2,

comprising a sleeve portion 53 and a portion 54 extending at rightangles thereto. The sleeve portion is made relatively long, as at agiven pressure, the leakage is substantially inversely proportional tothe length of the wearing ring; That is, with a given clearance betweenthe wearing ring and the flange of the impeller and a given flangediameter, the leakage from the high to the low pressure side of theimpeller is decreased upon increasing the length of the running tbetween the sleeve and the impeller ange.

In most wearing ring constructions, it is necessary to provide anappreciable diametral clearance between the sleeve and the impellerflange, of the order of ten to twenty thousandths of an times, slightlyoff center.

'portance because the leakage is but a small percentage of the volume ofliquid pumped. However, because, other factors being the same, theamount of leakage is substantially proportional to the pressure andsubstantially independent of the volume of the liquid being pumped, theleakage factor is very important in small capacity pumps. A leakage often gallons per minute is relatively unimportant in a'pump having acapacity of4 a thousand gallons per minute, but a leakage of ten gallonsper minute in a pump having a capacity of forty gallons per minute meansa loss of pump emciency from this source alone of twenty-ve per cent.

In accordance with my invention, the diametral clearance between thesleeve 53 and the flange 34 is made approximately ve thousandths of aninch which appreciably decreases the leakage from the high pressure tothe low pressure side as, in general, the leakage is proportional to thearea of the annular opening between the sleevev and the flange of theimpeller. Moreover, the shaft diameter and the weight of the impellerare selected and matched so that the maximum deflection of the shaftwill not exceed one thousandth of an inch which is insulilcient to causethe shaft to whip or rotate off center. Further,

I provide additional diametral clearance between from the high pressureside of the impeller tothe low pressure side thereof between the wearingring and the casing, the wearing ring is u free to be pressed againstthe casing by the pressure of liquid in the discharge chamber 5I.

` Figure 11.

T increase .the effect of this pressure, the portion 54 of the wearingring is provided with an annular sealing surface 62, as more clearlyshown in This annular sealing surface is of small' area. By reason ofthe pressure existing in the chamber I, when the pump is operating, thewearing ring is pressed toward the left, as viewed in Figure 2, so' thatthe annular sealing surface 62 is pressed into sealing engagement i withthe interior of the cover plate. The pressure between the sealingsurfaces vwill be the pressure Aof the liquid being pumped multiplied bythe effective area of thewearing ring exposed to discharge pressureAless the pressure on the suction side of the wearing ring times theeffective area of the wearing ring exposed to suction pressure dividedby the area of the annular sealing ring.

Of particular importance in the construction of my novel wearing ring isthe fact that the wearing ring is free to oat and will normally remainconcentric with the shaft sleeve, the additional clearance at 6I beingavailable to permit the wearing ring to adjust itself to compensate forany I charge chamber 5I aiaaevo eccentricity of the mating parts, suchas between the impeller flange St and the bore of the casing, andmaintain a uniform clearance between the impeller flange 3% and the boreof lthe wearing ring 52. While, in general, I am aware that the use offloating wearing rings has been considered before, I am aware of nowearing ring in 4which the importance of the clearances, above specifiedis recognized and in which the seal between the casing and the wearingring is accompished in the manner above described. Particularly, I amaware of no wearing ring in which the ring is locked in the casing toprevent its rotation with the pump impeller. In the floating Wearingrings with which I am familiar, the wearing ring'is' free to rotate withthe impeller and is likely to jam against the casing or impeller. In myconstruction, as shown more clearly in Figure 6, I provide on thewearing ring a lug 63 which registers with a notch 64 in the casing toprevent the wearing ring from rotating with the impeller and yet permitthe ring to oat freely.

In Figure 11, which is an enlarged View of a portion of the impeller andwearing ring of Figure 2, I haveI shown the wearing ring in engagementwith a shoulder 61 on the impeller, a possible position of the wearingring when the pump is not primed and there is no pressure differencebetween the discharge chamber 5| and the suction side of the impeller.With the wearing ring in this position, an annular throttling space orport 6B is provided between the wearing ring and the bore of the -casingthrough which leakage from the chamber 5i to the suction side of theimpeller may freely occur.

With the wearing ring in the position shown in Figure 1l, when the pumpis primed and develops discharge pressure, the capacity of the pump issumciently large that the leakage through the annular space 68 is notsufficient to drop the pressure in the chamber 5l appreciably. 'I'heleakage is a'so insufilcient to build up any appreciable pressure in thesuction chamber of the pump. Consequently, there is an unbalancedpressure area on the two sides of the wearing ring. That is, thatportion of the area. of the wearing ring represented by the differencein diameters K and L does not have equal pressures on opposite sidesthereof for the reason that the pressure in chamber 5I is greater thanthe pressure in the suction chsimber. Consequently, as the pressure invchamber 5I builds up, the wearing ring will move to the left, as viewedin Figure 1 1. The annular sealing surface 62 will then engage thecasing and cut olf the leakage through the throttling port 68. It isimportant that theparts be so constructed and arranged that the wearingring cannot move sufliciently far to the right, as viewed in Figure 1l,to permit open access between the disand the suction chamber. That is,the wearing ring at the limit of its possible movement to the rightshould be approximately in theposition shown in Figure 11,-with respectto the bore of the casing, so that ya small annular throttling space 68is provided.

In my close coupled pump, I have also provided novel means whereby thesame pump casing may be employed with shafts of various diameters. Inthe usual centrifugal pump construction, the stuffing box, indicated bythe numeral 69, is made integral with the casing and since the internaldiameter-.of the stuffing box is xed, only one diameter of shaft may beused with each pump casing. In my construction.

the shaft.

13, usually of bronze, of somewhatv smaller diam' eter than the diameterof the stuffing box bore. A plurality of rings of packing are insertedin the annular space between the internal bore of the stuffing boxandthe shaft sleeve.

As is usual in centrifugal pumps, a pipe connection 14 is providedconnected between the discharge chamber of the pump and a metal ring 'I5encircling the shaft and located in the bore of the stufng box.Sufficient pressure is applied on the packing rings to enable a slightleakage of uid to take place through the stuffing box in a direction tothe right, as viewed in Figure 2, to prevent air from entering the pump.A bronze casing wearing ring 16 of the ordinary type, fixed in a bore inthe stuiiing box and with respect to which the hub of the impeller isrotatable may be provided, although it will be appreciated that a casingwearing ring of the type described above may be substituted if desired.

Upon reference again to Figures 3, 4 and 10, it will be appreciated thatwith the flange 38 in the position sho-wn in Figure 3 with the dischargevalve 49 set to obtain 48 gallons per vminute at a total of 70 feet, themotor horsepower required by the pump will be approximately 1.6horsepower, which, in standard motors, would require the use of a twohorsepower 'motor unless an overloaded 1.5 horsepower motor 'inaccordance with the horsepower of the motor with which it is to beused.y A two horsepower motor naturally requires a larger diameter shaftthan a one horsepower motor. In order that the same pump casing may beused with a range of sizes of motors, it is therefore necessary that thepump casing be adapted by the means described above, or equivalentthereof, so that stuffing boxes having various 4bore diameters may beused interchangeably with the same pump casing.

In lthe stuffing box construction described above, the packing isretained in positionl by a 4packing gland 11 which, as is quite commonpractice, is made in two complementary parts secured together by bolts78. Upon removal of the bolts 18, the packing gland may be readilyremoved fromthe shaft. A solid type packing gland may be substituted, ifdesired, for the split and bolted type shown herein. Adjustable nut andbolt assemblies T8, extending between the stuiing box and thepackinggland, may be screwed up so that the part 8| which fits into thebore of the stuffing box may be pressed tightly against the packing. Abronze water singer 88, rigidly secured to the shaft by a set screw,prevents water from creeping along the shaftinto the mo- Icor bearings.

In the close coupled pump of my construction, I have provided novelmeans for retaining the impeller on the shaft and, at the same time,

preventing access of the liquid being pumped to This construction ismore clearly shown in Figure 8. 'I'he shaft sleeve 13 is coniinedagainst movement along the shaft in a direction to the right, as viewedin Figure 2, by butting it against a shoulder 82 on the shaft. The otherend of the shaft sleeve which, as is the usual practice, is made ofbronze, has a ta- "pered countersunk portion, as indicated at 83,

so as to provide an annularv bearing surface 84 cf restricted area whichis ground and finished.

A threaded bore 88 is provided in the end of the shaft along the axisthereof into which is threaded a socket head tap bolt 81 which has lwasher which engages the hubr of the impeller.v

The washer does not engage the shaft at any point.

In practice, particularly insmallpumps with which we are primarilyconcerned, since access to the bolt must be had through the eye orsuction opening of the impeller, the size of the bolt is, Within rathersmall limits, fixed by the diameter of the impeller suction opening.Moreover, the diameter of the shaft in small pumps does not permit theuse of a large diameter bolt and further, as isA apparent uponconsideration of Figure 2, a bolt with, a large diameter head restrictsthefree flow of `water through the impeller. With these considerations,limiting the size of the bolt, in mind, the bolt head and the diameterof the bolt at the root of the thread (the dimension N) are made aslarge as possible. Then, to obtain the maximum sealing pressure betweenthe annular sealing surface 9| of the washer 88 and the hub and betweenthe annular sealing surface 84 of the sleeve 13 and the hub, the areasof the sealing surfaces 9| and 84 are made equal to the area of thebolttfat the root of the thread.

When the bolt is tightened upv by a man, in the ordinary manner, so thatthe bolt is loaded within the elastic limit` of the material of thebolt, the pressure applied on the bolt is trans-.- mitted to the sealingsurfaces 9| and 84. This places the maximum pressure possible at theseal points without destroying the surface contacts between the sealingsurfacesand the hub. It will be appreciated that if the areas 9| and 84are made larger than the area of the'bolt at the root of the thread. thepressure at the sealing surfaces will not be the maximum amountpossible. If the areas 9| and 84 are made smaller p than the bolt areaat the root of the thread, then the pressure applied on the sealingsurfaces may be suiciently great to destroy the surface contacts at thesealing surfaces. When the sealing surfaces are loaded just within theirelastic limit, the whole area of the machined surfaces at the sealingpoints will be in contact because any slight unevenness of the surfaceswill be crushed out for the reason that the areas of these unevensurfaces will be less than the area of the bolt at the root of thethread and the sealing surfaces will imbed themselves slightly into thehub of the impeller. V The seal thus provided effectively prevents theliquid being pumped from gaining access to the shaft and is capable ofwithstanding a pressure of approximately 300 pounds per. square inch, apressure far above the pressure which the seals may be called upon towithstand. The shaft seal described eliminates the use of troublesomepacking. A copper seaiing ring d3 is interposed between the head o! thetap bolt 81 and the washer 89 which eiectively prevents leakage alongthe threads of the bolt. If desired, the bolt and washer may be madeintegral. Aiso if desired, instead of using a tap bolt threaded into athreaded bore in the shaft, as shown herein, the end of the shaft mayproject slightly beyond the hub of the impeller.. The projecting end maythen be threaded to receive a nut and there may be interposed betweenthe nut and the hub of the impeller a washer having a sealing surfaceengaging the hub of the impeller.

The hub of the impeller of the pump thus far described is provided withopenings 95 spaced around the hub so that the pressure on both sides ofthe hub will be the same and the impeller will, therefore, behydraulicallyl balanced since the pressure in the discharge chamber onopposite sides of the impeller are the same. In Figure 9 I have shownhow the shaft seal above described may be applied to an impeller inwhich the apertures through the huh of the impeller are omitted and theimpeller is, therefore, not hydraulically balanced. The construction isthe' same as that described above, differing therefrom only in theomission of the apertures and in the omission of an impeller wearingring corresponding to the wearing ring 1E of the structure shown inFigurez.

It will be appreciated that I have provided e. novel centrifugal pump ofthe close coupled type which is efiicient in operation, in which a noveimeans of sealing the drive shaft is employed and in which thecharacteristics of the pumpl may be readily varied to suit theconditions required, It will further be` apparent that features of myinvention may be readily incorporated in other types oi centrifugalpumps and that various modications may be made in the structure shownand described without departing from the spirit of my invention.

i claim:

1. In a pump of the class described, the combination of a casing havinga bore dening a peripheral hangs, a discharge outlet from said casing, avolute formed in said ange and can-l nected to the discharge outlet. arotatable impeller having a suction inlet adjacent its center, operablein said casing and discharging liquid peripherally into said volute, acover plate having a suction inlet in registry with the suction inlet ofsaid impeller, said cover plate having its periphery secured to thecasing flange, a ange integral with said cover plate and extending onlypart way around the cover plate, said ange forming a shroud around theimpeller and in-l sertable in said bore, with the vangeless portion ofsaid cover plate normally in registry with said volute portion of4 thecasing so that liquid may freely discharge from the impeller into saidvolute portion of the casing, said cover plate being shiftable withrespect to the casing so as to change the position of the ange on thecover plate with respect to the casing volute and thereby vary thecharacteristics of the pump.

2. In a pump ofy the class described, the combination of a casing havingan open side and having a discharge opening, a portion of the casingadjacent said discharge opening forming a ilxed cut-o, a voluteextending substantially from said cut-on part way around the innerperiphery of the casing and discharging into the discharge opening, arotatable impeller having a suction inlet adjacent its center operablein said casing and discharging liquid peripherally into said volute, acover plate removably secured to said casing adapted to close the openside of the casing and having a suction inlet in registry with thesuction inlet or said impelier, a fiange integral with and extendinginward from said cover plate and forming a shroud around the impeler,said ange extending oniy part way around the cover plate to denne flangeends, the space between the ends of the 'frange ming open and one end othe hangs normally lying adjacent the xed cut-od with the opening nor-1mally in registry with said volute whereby liquid may freely dischargefrom said mpeller into said volute, said cover plate being shiftablewith respect to the casing to shift the end of the ange

